This invention relates to inkjet printers and the like, and more particularly to an inkjet printing system that makes use of multi-pass printing to form images and text on print media.
Inkjet printing systems frequently make use of an inkjet printhead mounted to a carriage which is moved back and forth across print media such as paper. As the printhead is moved across the print media, a control device selectively activates a plurality of drop generators within the printhead to eject or deposit ink droplets onto the print media to form images and text characters. An ink supply that is either carried with the printhead or remote from the printhead provides ink for replenishing the plurality of drop generators.
Individual drop generators are selectively activated by the use of a select or an enable signal that is provided by the printing system to the printhead. In the case of thermal inkjet printing, each drop generator is activated by passing an electric current through a resistive element such as a resistor. In response to the electric current the resistor produces heat, that in turn, heats ink in a vaporization chamber adjacent the resistor. Once the ink reaches vaporization, a rapidly expanding vapor front forces ink within the vaporization chamber through an adjacent orifice or nozzle. Ink droplets ejected from the nozzles are deposited on print media to accomplish printing.
The electric current is frequently provided to individual resistors or drop generators by a switching device such as a field effect transistor (FET). The switching device is activated by a control signal that is provided to the control terminal of the switching device. Once activated the switching device enables the electric current to pass to the selected drop generator or resistor. The electric current or drive current provided to each resistor is sometimes referred to as a primitive signal and a control signal for selectively activating the switching device associated with each resistor is sometimes referred to as an address signal.
In one previously used arrangement, a plurality of primitive signals are provided with each of the plurality of primitive signals connected to a different group of drop generators within the inkjet printhead. Each of a plurality of address signals is provided to each switching device associated with each drop generator. Using this technique a drive signal is provided to each primitive containing a drop generator that is to be activated. The address signal is provided to each primitive to select the particular drop generator for activation within the primitive or grouping of drop generators. The use of this technique reduces the number of signals required to uniquely select and activate individual drop generators.
The above-described scheme for activating selected drop generators within the inkjct printhead is susceptible to certain failure modes that can result in deleterious effects on print quality. For example, a failure of one of the address lines to provide an address signal to each of the primitives or groupings of drop generators results in a failure of each drop generator associated with that particular address line in each primitive. The problem tends to be further exacerbated in printheads that have larger numbers of drop generators. These printheads tend to have larger numbers of primitives producing larger number of drop generator failures because each address line is connected to a drop generator in each primitive.
An address line can fail to provide a proper address or enable signal to drop generators in each of the primitives in several ways. Because each address signal is received from the inkjet printing system, a failure of the electrical interconnect between the printer portion and the printhead can produce a failure of one or more address lines. The electrical interconnect between the printhead and the printing system can fail as a result from improper seating during the installation of the print cartridge or from corrosion or contamination on one or more electrical contacts associated with either the printing system or the print cartridge. Improper seating or corrosion can result in either no electrical interconnect or a high resistance electrical interconnect between the printing system and the ink cartridge. If this electrical contact between the printing system and the ink cartridge is sufficiently high resistance, then the address signal will be sufficiently attenuated to prevent proper activation of the drop generators associated with this address line.
Another cause of an address line failure is failure in the electrical interconnect between the flexible circuit and the contact pads on the printhead. Frequently, an electrical interconnect such as a flexible circuit is used to route signals from the contact pads that are configured for connection to the printing system and a silicon substrate on which the drop generators are defined. Tape automated bonding (TAB) is frequently used to form the electrical interconnect between the flexible circuit and contact pads on the silicon substrate. Failure of this TAB bonding to form good electrical connection between the flexible circuit and the silicon substrate can produce an address line defect.
Finally, various defects on the printhead itself can also result in the failure of address signals in reaching the corresponding drop generators. One example of a die defect is a failure in one or more layers of the printhead to properly channel ink to desired locations on the die which can result in ink shorts or low resistance electrical paths. These electrical paths or ink shorts can attenuate an address signal sufficiently to prevent proper activation of the corresponding drop generators.
There is an ever-present need for inkjet printing systems that produce high print quality and which are highly reliable. These inkjet printing systems should be well-suited for high volume manufacturing in order to provide relatively low per page printing cost.